<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    let arr=[1,2,3,4,5,4,3,2,1]
    // 1.数组去重
    let result=[...new Set(arr)]
    console.log(result)

    // 2.交集
    let arr2=[4,5,6,5,6]
    // let result2=[...new Set(arr)].filter(item=>{
    //     let s2=new Set(arr2)
    //     if (s2.has(item)){
    //         return true
    //     } else {
    //         return false
    //     }
    // })
    let result2=[...new Set(arr)].filter(item=>new Set(arr2).has(item))
    console.log(result2)

    // 3.并集
    let union=[...new Set([...arr,...arr2])]
    console.log(union)

    // 4.差集
    let diff=[...new Set(arr)].filter(item=>!(new Set(arr2).has(item)))
    console.log(diff)
</script>
</body>
</html>
